How exactly is a purple tang, koran angel, copperband butterfly, and 2 percs in a 55 ideal? A koran angel can get up to 15 inches, the purple tang will get pretty big and needs alot of room, and the butterfly gets big too. None of them should be in a 55g tank for long, let alone life. If you are upgrading very soon, fine, but if you aren't, then you are in for some trouble very soon.